Ultrasonic spectroscopy uses ultrasonic energy to inspect defects and/or material properties of test materials. An ultrasonic inspection system includes ultrasonic transducers to deliver ultrasonic energy to, and detect ultrasonic energy from, the test materials. The ultrasonic inspection system analyzes the detected ultrasonic energy using ultrasonic spectroscopy techniques to expose the defects and the material properties. It is desirable to be able to deliver the ultrasonic energy to the test materials over a wide range of ultrasonic frequencies, frequency bandwidths, and amplitudes matched to a variety of properties of the test materials and operating characteristics of different transducers; however, conventional ultrasonic inspection systems operate over only a relatively narrow range of ultrasonic frequencies, frequency bandwidths, and amplitudes and suffer from both frequency and amplitude impairments outside of these narrow confines. As a result, conventional ultrasonic inspection systems limit the types of transducers that may be used and the variety of test materials that may be inspected.
Ultrasonic spectroscopy techniques may be performed on test material in the form of a single layer structure or a multilayer structure to identify/characterize composition, defects or damage in one or more layers, or bonding failures or separation between adjacent layers in a multilayer structure. One ultrasonic spectroscopy technique determines frequency responses, including material resonances in the detected ultrasonic energy. Another technique identifies time pulses in the detected ultrasonic energy. Ideally, frequency resonances are distinct from each other and the pulses are distinct from each other. In practice, however, the detected ultrasonic energy is complex because it includes time-overlapped ultrasonic energy reflections and reverberations from/caused by the different layers within the multilayer structure or a significant defect in a single layer structure. This results in destructive and constructive interference in the detected ultrasonic energy, which makes detecting distinct time reflections very difficult.